General Chemistry Exam Study Guide: Kinetics, Equilibrium, Acid-Base, and Laboratory Calculations

Kinetics and Rate Laws

Introduction to Reaction Rates

Chemical kinetics studies the speed at which chemical reactions occur and the factors that affect these rates. The rate law expresses the relationship between the rate of a reaction and the concentration of its reactants.

• Rate Law: An equation that links the reaction rate to the concentrations of reactants, often in the form $\text{rate} = k[A]^m[B]^n$.

• Order of Reaction: The power to which the concentration of a reactant is raised in the rate law.

• Example: For the reaction $N_2(g) + 3Cl_2(g) \rightarrow 2NCl_3(g)$, experimental data is used to determine the rate law by comparing initial rates and concentrations.

Experimental Determination of Rate Laws

• Method: Use initial rates from multiple trials with varying reactant concentrations.

• Calculation: Compare how changes in concentration affect the rate to deduce reaction order for each reactant.

• Example Table:

Trial	[N2]	[Cl2]	Rate (M/min)
I	0.200	0.300	0.100
II	0.200	0.600	0.200
III	0.400	0.300	0.200

Acid-Base Equilibria

pH and pOH Calculations

Acid-base chemistry involves calculating the concentration of hydrogen ions ($[H^+]$) and hydroxide ions ($[OH^-]$) in solution, and using these to determine pH and pOH.

• pH Formula: $\text{pH} = -\log[H^+]$

• pOH Formula: $\text{pOH} = -\log[OH^-]$

• Relationship: $\text{pH} + \text{pOH} = 14$ (at 25°C)

• Example: Mixing solutions and calculating final $[OH^-]$ concentration.

Acid and Base Dissociation Constants

• Ka (Acid Dissociation Constant): Measures the strength of an acid in solution.

• Kb (Base Dissociation Constant): Measures the strength of a base in solution.

• ICE Chart: Used to calculate equilibrium concentrations and constants.

• Example: Calculating $K_a$ or $K_b$ from initial concentration and percent dissociation.

Equilibrium Calculations

Equilibrium Constant (K)

The equilibrium constant quantifies the ratio of product to reactant concentrations at equilibrium for a reversible reaction.

• Expression: $K = \frac{[\text{products}]}{[\text{reactants}]}$ (raised to their stoichiometric coefficients)

• ICE Table: Initial, Change, Equilibrium concentrations are used to solve for unknowns.

• Example: Calculating $K_{eq}$ for a reaction using measured equilibrium concentrations.

Laboratory Calculations and Techniques

Titration and Standardization

Titration is a technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

• Equivalence Point: The point at which the amount of titrant added is stoichiometrically equivalent to the amount of analyte in solution.

• Calculation: Use volume and molarity to find moles of reactant.

• Example: Calculating the concentration of NaOH in a buret from titration data.

Percent Composition and Molar Mass

• Percent by Mass: $\text{Percent by mass} = \frac{\text{mass of solute}}{\text{total mass of solution}} \times 100\%$

• Molar Mass: The mass of one mole of a substance, used in stoichiometric calculations.

• Example: Determining the percent by mass of HCl in a sample using titration results.

Safety in the Chemistry Laboratory

Laboratory Safety Practices

Proper safety procedures are essential when working with chemicals and glassware in the laboratory.

• Key Practices:

  • Always wear safety goggles and appropriate clothing.

  • Do not wear open-toed shoes or sandals.

  • Tie back long hair and avoid loose clothing.

  • Never eat or drink in the laboratory.

• Example: Identifying unsafe practices such as wearing shorts or open-toed shoes.

Reference Information

Periodic Table and Constants

The periodic table provides essential information about elements, including atomic numbers and symbols. Key constants and equations are often provided for reference during exams.

• Example Equations:

  • $A = -\log T$

  • $A = \epsilon c C$

  • $\text{rate} = k[OH^-][CV]$

  • $\text{pH} = pK_a + \log \frac{[A^-]}{[HA]}$

• Periodic Table: Used to identify elements and their properties for calculations.